Commutating brush



Dec. 29, 1936. GlRVlN ET AL 2,065,176

I COMMUTATING BRUSH I Filed Sept. 27, 19:55

Iml ore matecl with a X {j} resinous compos'rbioh m f Car-ban and hydr-ccar-bon binder" Inventors: Fred Gir-vin, William H. Hardrnah,

Their Attorney.

. titers Patented Dec. 29, 1936 UNITED STATES PATENT OFFICE COMJWUTATING BRUSH Fred Girvin and William H. Hardman, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application September 27, 1935, Serial No. 42,431

6 Claims. (Cl. 171-325) The present invention relates broadly to brushes for use in electrical apparatus and more particularly to improved commutating brushes.

It is an object of our invention to provide an improved electrical commutating brush having a cent by weight of a hydrocarbon binder, such as pitch or coal tar. The mixture is compacted into desired form and fired to a temperature around 1370 C. for about 58 to 60 hours to completely carbonize the binder. An additional graphitizing low sparking tendency, high mechanical strength heat treatment at 2500-3000 C. for 5-10 hours 5 and definite resistivity. may be employed to improve the conducting Electrical brushes made from carbon bonded properties of the brush. The porous molded with hydrocarbon compounds have long been in brushes next are impregnated by being placed on 10 use. The carbon in this type of brush is ordiend in a shallow bath of synthetic resin. The 10 narily loosely bonded together thereby lowering degree of impregnation can be controlled by the the tendency to spark. However, porous brushes temperature of the bath and the time of immerconsisting merely of carbon loosely bonded tosion. Brushes having the end impregnated for gether with hydrocarbon compounds have been example up to 0.5 inch for one hour at a temperrestricted in use due to their mechanical weakature of about 50 to 55 C. have been found 15 ness. Brushes of this type frequently fracture satisfactory. at the end held by the pressure arm. The molded impregnated brushes are again Electrical brushes made from carbon bonded fired to a curing temperature around 175 to 250 with various synthetic resins have also been in C. for about 24 hours. The temperatures reuse. While brushes of this type containing a quired to cure the resin vary with the particular 20 high percentage of synthetic resin may possess resin composition. good mechanical strength, the carbon is closely It has been found that brushes impregnated bonded giving a non-porous brush which blackens with synthetic resins of the vinyl and alkyd types and burns as a result of excessive sparking parhave excellent electrical and mechanical proper- 25 ticularly when used in a commutating or collectties. The vinyl resins consist usually of poly- 25 ing capacity. Moreover, electrical brushes com- I r 1 e1;ized vinylpompounds such for example as a posed of carbon bonded with synthetic resin have combination of pely nfiariied vinyl chloride and also found restricted use as the resin decomposes polymerize ilinylg etate. Th' alkydresins are when subjected to high commutating temperacomposed of reaction products formed from a tures. On decomposition of the resin, this type polybasic acid, such as phthalic acid or its anhy- 30 of brush is easily cracked and broken. dride, and a polyhydric alcohol, such as glycer- It has been proposed to strengthen the brush ine, with or without various modifying agents. by the introduction of various foreign ingredi- The synthetic resin impregnated brushes made in ents. For example, the use of clay and other accordance with our process are not subject to inorganic binders h v n su st d. us s decomposition for while the commutator contact- 35 constructed in this manner have not been found 1 d of the brush may reach high temperaentirely satisfactory for all applications as the tures t end held by t pressure arm containmixing of foreign ingredients With the carbon ing the synthetic resin remains relatively cool. have been acco p by a l e in the elee- While the brushes constructed in accordance 4O trical resistance. A brush combining low tendwith our process have porous commutator 40 toward e i l high mechamca'l Strength tacting tips which lower tendencies toward z' gggg l f gfi gi therefore long been sparking, the impregnated end held by the pres- We have discovered that when the conductory 1s gg g arfld meuharllgpany of contacting or clamping end of a porous commu- F S rang. 0 e ree cmc mg or 4 tating brush consisting of carbon and: a hydro mg tendencies. The resistivity of the brush is carbon binder is impregnated with a synthetic also easily controlled as the impregnation of the resin and cured so as to set the latter, the brush to be held by the pressure am (not shown) possesses the advantages enumerated above. Wlth the small percentage of resin does not p- The accompanying drawing shows a commu- Preciably change the conductivity 50 tating brush made in accordance with our inven- Although We ave described our invention tion. enumerating certain specific ingredients, we do According to our invention carbon in the form not wish to be limited thereto as various equivaof pulverized coke, graphite, lamp black or the lents coming within the scope of our invention like, is mixed thoroughly with about 30 to 35 per are meant to be covered in the appended claims. 55

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. A molded commutating brush having a porous commutator contacting end of loosely bonded carbon, and a non-porous conductor contacting end composed of a closely bonded carbon impregnated with a resinous composition.

2. A commutating brush free from sparking tendencies composed of carbon and carbonized hydrocarbon binder and having the end adapted to be held by a pressure arm, closely bonded with a cured synthetic resin.

3. A molded commutating brush consisting of graphite bonded with carbonized hydrocarbon binder and having the conductor contacting end impregnated with vinylresirr.

4. A molded commutating brush consisting of graphite bonded with carbonized hydrocarbon binder and having the end adapted to be held by a pressure arm, impregnated with alkyd resin.

5. The process of making a brush for use with electrical apparatus, which comprises thoroughly mixing carbon with a hydrocarbon binder, compacting the mixture into desired form, firing at a temperature and for a time sufficient to completely carbonize said hydrocarbon binder, impregnating the end of the porous loosely bonded brush to be held by the pressure arm with a resinous composition and heating the brush at a temperature and for a time sufiicient to cure said 6. The process of making an electrical brush having improved commutating characteristics, which comprises thoroughly mixing carbon with about to per cent by weight of hydrocarbon binder, molding the mixture into the desired form, firing at a temperature and for a time suflicient to completely carbonize said hydrocarbon binder, impregnating the end to be held by a pressure arm with a synthetic resin and heating the brush at a temperature and for a time suflicient to cure s aid-resin.

FRED GIRVIN.

WILLIAM H. HARDMAN. 

